First, Marielle Franco was gunned down in an apparent organised hit, prompting tens of thousands of Brazilians to protest. Then came the character assassination.

The immediate reaction to the killing March 14 of the Rio de Janeiro city councilwoman was raw and spontaneous. Huge crowds took to the streets in Rio and in Sao Paulo, with smaller demonstrations in cities around Brazil and the world.

Franco was held up as an example of a black Brazilian who overcame racism and poverty, inspiring millions with her courageous stand for human rights in Rio’s dangerous favela neighborhoods. She was a political martyr.

Or was she actually a drug user?

Could it be she’d once married a drug gangster called Marcinho VP? Had her much vaunted election to the city council been funded by Rio’s terrifying narco group Red Command?

It took a blink of the social media eye for the narrative around Franco to switch direction.

Twitter, Facebook and WhatsApp – all hugely popular in Brazil – lit up with claims that the 38-year-old was not the saintly figure claimed.

“Check out the left’s latest myth, Marielle Franco. Pregnant at 16, ex-wife of Marcinho VP, she used marijuana…, was elected by the Red Command, had just fired six employees,” tweeted congressman Alberto Fraga, from the small, rightwing DEM party.

The story about Franco’s deep criminal past flooded the internet, often expressed in furious language, but lent gravitas by the likes of Fraga.

A Rio appeals’ court judge called Marilia Castro Neves warned on Facebook that Franco “wasn’t just a fighter.”

No, she “was involved with bandits” and was killed because “she didn’t carry out her promises.”

Startling stuff. Shocking.

And totally fake.

Setting the record straight

The rumor mill works at lightening speed in Brazil, one of the world’s most social media-addicted countries. It’s also a country deeply divided between left and right, and richer whites and poorer blacks.

Franco had made plenty of enemies on the right with her prominent accusations of police brutality in the favelas. Some, for example, asked angrily why Franco and her supporters were not more concerned about the astonishing number of police officers killed in Rio – more than 100 last year.

So the attempt to transform her from rights campaigner to criminal sympathizer fell on fertile ground.

“This was an orchestrated campaign, not just one or two people saying bad things,” said Cristiane Costa, coordinator at the Federal University of Rio de Janeiro’s journalism school.

Yet the reaction to the backlash was even more powerful, showing how the fake news virus can be fought.

Lawyers with Franco’s leftist PSOL party have appealed online for tips on fake news posts, which they then identify and refer to the police. By the start of this week, they’d got more than 15 000 emails in response, G1 news site reported.

Others are responding directly.

“Let me say a few more things,” Franco’s sister Anielle Silva, wrote on her Facebook page.

“Marielle was not a bandit and much less a defender bandits. Marielle was never married or involved with Marcinho VP, Marielle never was a drug user, and Marielle was not financed by any gang.”

The post was liked by 140 000 people.

Franco’s family also built a page on the late councilwoman’s website called “The truth about Marielle,” carefully rebutting each item of fake news.

And the traditional media, which Costa says has “the tools to check rumors very quickly,” also joined the cause.

Globo newspaper, part of Brazil’s dominant media conglomerate, ran a full page Tuesday to shoot down the rumors, under the headline: “Lies cannot stop justice.”

Fraga deleted his tweet.

“The regret, perhaps, is having put something that I didn’t check,” said Fraga. “I am a police officer, a military colonel, I should have had better information and from an appropriate source.”

As for the judge, she says she wishes she had decided “to wait for the end of the investigation, so as to be able, as a citizen, to give my opinion.”